The reaction of isopropylbenzene with bromine under light is a radical reaction. The light initially reactions with the bromine in the initiation step to form the bromine radicals:
Br₂ + hv → 2Br·
The next step is the first propagation step where a bromine radical reacts with the isopropylbenzene to abstract the hydrogen from the tertiary carbon in the isopropyl group:
We have now formed a radical in the benzylic position of the isopropylbenzene structure. Now this radical will react with another molecule of bromine in a second propogation step to form the final brominated product:
The bromine radical can terminate in a reaction with another bromine radical or the benzylic radical to give more of the final product. The final product is shown and is called (2-bromopropan-2-yl)benzene.
Actually, the
uncertainty point is when we have to estimate one place smaller than what the
graduated cylinder can accurately read. So in this case, the smallest that we
can accurately read is given by the minor marks of 0.2 mL. So if it is in
between two minor marks we can only estimate the number, therefore the
uncertainty is +/- 0.1ml.